data.json

{
    "languages": {
        "python": {
            "name": "Python",
            "author": "Guido Van Rossum",
            "usedFor": ["Scripting", "Web Development", "Text processing", "Data Science"]
        },
        "go": {
            "name": "Go",
            "author": "Google",
            "usedFor": ["Devops Tooling", "Low-latency Servers", "command-line Tools"]
        }
    }
}

json_decoder.py

import json

fp = open("data.json", "r")

# Custom decoder function
def add_count_to_decoded_dict(obj):
    if "usedFor" in obj:
        # populate a new field `usageCount` while de-coding JSON
        obj["usageCount"] = len(obj["usedFor"])

    return obj

result = json.load(fp, object_hook=add_count_to_decoded_dict)

if "languages" in result:
    languages = result.get("languages")

    if "go" in languages:
        golang = languages.get("go")
        name = golang.get("name")
        count = golang.get("usageCount")

        # Prints 'Go is mainly used for 3 reasons'
        print(f"{name} is mainly used for {count} reasons")